Precambrian Basement of the Congo Basin and Its Flanking Terrains - Geology and Resource Potential of the Congo Basin - page 32

2.4.4.4 The Mozambique Belt
The Mozambique Belt of northeastern Mozambique flanks
the eastern margins of the CAS and the Southern African
Shield at Africa

assemblage inculcates peripheral (outcropping) Archean
nuclei: the Kasai, Cuango, Ntem, Bouca and Mboumou-
Uganda cratonic blocks that constitute three larger Congolese
Cratons largely unexposed beneath the CB: the SouthWest-,
the Cuvette- or Central- and the NorthEast- Congo Cratons
(SW-, C- and NE -CC) and that in turn, together, constitute
the Congo Shield (CS). Subsequently these three aggregated
along the Central Angola Mobile Belt (CAMB; ca.
2.0-2.3 Ga; Carvalho et al. 2000 ) and the West Central
African Mobile Belt (WCAMB; ca. 2.0-2.5 Ga, Feybesse
et al. 1998 ) to form the SouthWestern Congo Shield
(SWCS). In the east, the CS enlarged further to form the
Central African Shield (CAS) during the Proterozoic along
Eburnian, Kibaran and Pan-African orogenic belts (Fig. 2.6 ),
but the details of the accretion processes of these continental
domains remain uncertain. The working model we provide
here serves only to open discussions and encourage renewed
field work and radiometric dating across this region, as that
catalysed by Arthur Holmes, William Kennedy, Luiz Cahen
and Norman Snelling in the last century. There is much work
to be undertaken before a robust model for the formation of
the CAS can emerge.
The basement beneath Phanerozoic CB is clearly com-
plex. The oldest Archean cratons may have amalgamated in
the Proterozoic, although the precise age of amalgamation is
in dispute, and may even have occurred in the Archean. Parts
of these cratons are exposed along the northern, southern and
eastern margins of the CB, where they are flanked by
Eburnian and Pan-African sequences; and the Tanzanian
Craton (with its remobilised Archean crust to the west,
within the northern Mozambique belt), which collectively
is referred to here as the CAS.
The southern margin of the CS is defined by the Central
Shield Zone of Angola, a wide transition zone of Eburnian
granitoid magmatism and high-grade tectonism that also
embodies a number of Archean fragments, and which we
have named the CAMB, inferred to represent a deep,
exhumed Himalayan-style Eburnian orogenic belt. This
belt separates the rest of the Angola basement to the south,
comprising predominantly Eburnian-Kibaran (mid-Protero-
zoic) Tibetan-like crust, from the SWCC. These two blocks
collided along the CAMB at ca. 2 Ga to form the SWCS.
Between the Tanzanian Craton and the CS, a complex
Eburnian-Kibaran tectonic history includes large scale melt-
ing of Eburnian crust between 1.3-1.5 Ga. Near the southern
margin of the Angola basement, the vast Mesoproterozoic
mafic-anorthosite complex of Kunene associated with wide-
spread red granites and syenites dated around 1.3-1.4 Ga Ma
confirm Kibaran (s.s.) mafic and granite magmatism and
large scale crustal melting along the southern margin of the
CS that may link along a continental shear zone to the type
Kibaran of the Karagwe-Ankole Belt (Fig. 2.6 ). Subsequent
accretion of other crustal blocks, along a number of orogenic

'

s southernmost extent of the Pan-African
East African Orogen. Details of this orogen are beyond the
scope of this chapter, but the interested reader is referred to
Fritz et al. 2013 , and references therein). Suffice it to men-
tion that the Mozambique Belt yielded the first 1.0 Ga
Kibaran (Mozambican) dates on orthogneisses and high
grade granulites in Africa (Holmes 1918 , 1951 ), an age
which has since been recorded by Rb/Sr analyses (e.g.
Cahen et al. 1984 ), and more recently confirmed by precise
zircon and monazite dating (e.g. Jamal 2005 ; Bingen et al.
2009 ; Fritz et al. 2013 ). For example, the Mozambican
orthogneisses of the Unango and Marrupa complexes date
between ca. 946 Ma and 1062 Ma, overprinted by the exten-
sive Pan-African high grade granulite-facies metamorphism
with charnockitization between 700-525 Ma (Fig. 2.2 , Inset
B; Jamal 2005 ). These lower crustal rock types and ages
have strong affinities with similar rocks of southern India
and Madagascar. All these regions are similarly overprinted
by extensive Pan-African deformation dated between
530-620 Ma. Whilst in detail the Kibaran/Pan-African his-
tory is complex (Jamal 2005 ; Bingen et al. 2009 ; Fritz et al.
2013 ), there is justified reason here for mentioning these
Kibaran/Pan-African dates of the Mozambique Belt, because
in many of the Phanerozoic sequences of the CB, detrital
zircon analyses invariably yield both abundant ca. 1.0 Ga
and 0.6 Ga dates (Linol et al., Chaps. 7 and 8 , this Topic). To
date, the source of this bimodal detrital zircon population has
been controversial. Since the age of crystalline rock-types of
the Mozambique Belt is similar to parts of the Oubanguides
flanking the northern margin of the CAS, and the regions to
the north (in Central Sahara), the detritus may have been
sourced from either north of the CB (Fig. 2.2 , Inset A; e.g.
Linol et al. 2014 , submitted) or southeast of the CB (Fig. 2.2 ,
Inset B; e.g. Roberts et al., 2012). Only when integrated with
sedimentology data (paleocurrent directions) can a conclu-
sive interpretation for a northerly source of many CB
sequences be verified (see Linol et al., Chaps. 8 , 9 and 13 ,
this Topic).

2.5 Summary and Conclusions

The CB of central Africa is underlain and completely
surrounded by Precambrian basement that spans a history of
up to 3.8 Ga, including Archean cratonic blocks, with rocks
along its northeastern edge possibly as old as 4.0 Ga (and
detrital zircons of similar age on the Tanzanian Craton),
separated and surrounded by numerous Paleo- to Neo-
Proterozoic mobile belts. Diamondiferous kimberlites span
a range of almost 3.0 Ga billion years. This complex